Kuro has long, flowing reddish-brown hair, with a strand that stands up at the top. She is usually dressed in a light brown hoodie with a brown hood with no bottoms as her hoodie covers the length of her body. She keeps her dog, Puni Puni, in front of her hoodie with Puni Puni's head stuck out. She also wears a dog collar around her neck. She has boxing bandages wrapped around her hands and feet but later wears black gloves and black open toe socks.

In the second half of Kurokami, she wears a qipao with longer black sleeves, and socks

Keita and Kuro met at a makeshift ramen stall one night when the hungry Kuro stumbled on the stall. Seeing that Kuro really wanted a bowl of ramen, Keita gives his bowl up to her, which makes her grateful to Keita for his act of kindness. While Kuro was eating her ramen, a tribal end approaches and hits her, overturning her bowl of ramen. Angry, Kuro fights and defeats the tribal end. In the manga, Keita's arm is cut off during this encounter and he passes out. Kuro then switches arms with Keita to save him, forming a contract with Keita. In the anime, Keita is injured severely during their encounter with Senji and Kuro trades hearts with Keita, forming a contract.

Kuro has a crush on Keita, proving so in Episode 22 of the anime, though she never confessed how she felt to Keita. She breaks down in tears before leaving for the Pure Place, stating that she loved Keita.

As Keita reaches the end of his human lifespan and dies, their pact ends and the Exceed crests on both Kuro and Keita's hands fade. As Keita dies, Keita thanks Kuro through their communication. Kuro thanks him for their relationship and is glad he was able to live a happy life, wishing him to rest in peace as her beloved contractee.

Her manga version fights using boxing, having learned it from a former professional boxer, while her anime version does not have any particular style. Both, however, use an Exceed which massively increases her offensive power. In the anime, her exceed is the Mega-exe, though in episode 16 it changes to Giga-exe when Keita and Kuro connect their Tera to become one. In episode 22, when Keita and Akane combine Tera Energy to allow her to perform Terra Exe, the ultimate Exceed attack.